Smart valve utilizing a force sensor

ABSTRACT

A valve, in certain embodiments, includes a body having a flow path, a stem, a flow element coupled to the stem, wherein the flow element interfaces with the flow path to regulate flow of a fluid through the flow path, and a force sensor coupled to the stem and configured to indicate an amount of force exerted on the stem.

FIELD OF INVENTION

The present invention relates to regulation and monitoring of fluidflow. More particularly, the present invention relates to a smart valvefor monitoring valve performance and for measuring the pressure of aprocess fluid flowing through the smart valve.

BACKGROUND

This section is intended to introduce the reader to various aspects ofart that may be related to various aspects of the present invention,which are described and/or claimed below. This discussion is believed tobe helpful in providing the reader with background information tofacilitate a better understanding of the various aspects of the presentinvention. Accordingly, it should be understood that these statementsare to be read in this light, and not as admissions of prior art.

The use of valves to manage and transmit materials is ubiquitous. Valvesgenerally include an open position that enables fluid flow and a closedposition that reduces or completely shuts off the fluid flow. Monitoringof conditions (e.g., flow and pressure) of the fluid flowing through thevalve is generally desirable. In addition, monitoring of performance ofthe valve is also generally desirable. In particular, during the life ofthe valve, its condition and performance may typically degrade. Further,the valve may foul due to adverse process conditions, for example.Consequently, the valve may be repaired or replaced.

BRIEF DESCRIPTION OF THE DRAWINGS

Various features, aspects, and advantages of the present invention willbecome better understood when the following detailed description is readwith reference to the accompanying figures in which like charactersrepresent like parts throughout the figures, wherein:

FIG. 1 is a front view of a smart valve which may incorporate a forcesensor in accordance with an embodiment of the present invention;

FIG. 2 is a cross-section of the smart valve taken along line 1-1 ofFIG. 1 that depicts the smart valve in a closed position in accordancewith an embodiment of the present invention;

FIG. 3 is a cross-section of the smart valve taken along line 1-1 ofFIG. 1 that depicts the smart valve in an open position in accordancewith an embodiment of the present invention;

FIG. 4 is a cross-section of the smart valve taken along line 1-1 ofFIG. 1 that depicts the smart valve transitioning from a closed positionto an open position in accordance with an embodiment of the presentinvention;

FIG. 5 is a flow chart of a method for determining a pressure of aprocess fluid using the smart valve in accordance with an embodiment ofthe present invention; and

FIG. 6 is a flow chart of a method for determining the performance orother condition of the smart valve in accordance with an embodiment ofthe present invention.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

One or more specific embodiments of the present invention will bedescribed below. These described embodiments are only exemplary of thepresent invention. Additionally, in an effort to provide a concisedescription of these exemplary embodiments, all features of an actualimplementation may not be described in the specification. It should beappreciated that in the development of any such actual implementation,as in any engineering or design project, numerousimplementation-specific decisions must be made to achieve thedevelopers' specific goals, such as compliance with system-related andbusiness-related constraints, which may vary from one implementation toanother. Moreover, it should be appreciated that such a developmenteffort might be complex and time consuming, but would nevertheless be aroutine undertaking of design, fabrication, and manufacture for those ofordinary skill having the benefit of this disclosure.

The disclosed embodiments include a smart valve, which includes a forcesensor (e.g., load sensor, load cell, strain gauge, and so forth) tomonitor the force (or pressure) exerted on the stem of a valve member.Incorporation of the force sensor facilitates monitoring of valveperformance throughout the life of the valve, as well as monitoring ofthe flow line (e.g., process) pressure. In addition, the flow linepressure (i.e., the pressure of the process fluid being regulated by thevalve) may be monitored both when the valve is in a shut-in condition(e.g., no fluid flow through the valve flow path) and when the valve isin an open position. In other embodiments, the flow line pressure mayotherwise be monitored via a pressure gauge, pressure transducer, orother pressure element installed directly into the flow path of thevalve. A benefit of using the force sensor to monitor flow pressure isthe elimination of a possible leak path associated with an instrumenttap (i.e., with a pressure gauge) installed directly in the flow line,for example.

Valve performance may be evaluated by the amount of supplied pressureneeded to actuate the valve, or by disassembling the valve to inspectinternal parts, for example. In contrast, incorporation of the forcesensor in the valve will generally provide for improved monitoring ofthe valve performance without disassembly of the valve. The sensed forceinformation may be employed to alter the maintenance program of thevalve, for example. In addition, the force sensor may be employed tomonitor the flow line pressure (i.e., the pressure exerted by theprocess fluid in the flow path of the valve) via the pressure acting onthe valve stem's cross sectional area. Further, as discussed below,incorporation of a displacement transducer in the valve to measure stemmovement may provide additional information with regard to valveperformance. The disclosed embodiments may be applied to existingdesigns with relatively minor modification in certain applications.Examples of the smart valves disclosed herein may include flow valves,gate valves, butterfly valves, plug valves, ball valves, needle valves,and so on. Whatever the type of valve, it is generally beneficial tomonitor the performance of the smart valve, as well as to obtaininformation about the fluid the smart valve is regulating.

FIG. 1 is a front view of a smart valve 10 which may incorporate a forcesensor in accordance with an embodiment of the present invention. Thesmart valve 10 may include a valve body 12 coupled to a valve bonnet 14via one or more bolts 16. The smart valve 10 may also include anactuator assembly 18 that, as described below, may be used to move avalve stem of the smart valve 10 axially along a central axis 20 of thesmart valve 10 to actuate the smart valve 10 between open and closedpositions. The actuator assembly 18 may be operated by a human operator(e.g., using an override tool) or may be automatically operated by ahydraulic or electric drive system.

The smart valve 10 also includes an inlet passage 22 and an outletpassage 24 to provide connection to piping or other components. Forexample, the smart valve 10 may be placed between an upstream pipe 26transporting a process fluid from a source and a downstream pipe 28transporting the process fluid to downstream equipment. In such anembodiment, the smart valve 10 may be used in an on/off manner to allowor block flow from the upstream pipe 26 through the smart valve 10 andinto the downstream pipe 28. In other embodiments, the smart valve 10may be used to regulate (e.g., choke) flow from the upstream pipe 26into the downstream pipe 28.

The materials of the smart valve 10 may vary considerably, depending onthe specific applications, for example. Valve materials may includecarbon steel, stainless steel, low alloy steel, nickel plated materials,nickel alloys (e.g., iconel, monel, and the like), Teflon inserts, andso forth. Sealing and gasketing materials may include Teflon, PTFE,elastomers, metals, and so forth. The pressure and temperature ratingsof the smart valve 10 may also vary considerably, depending upon theparticular application. Moreover, such ratings are not intended to limitthe present techniques, which may be used for any flow line pressure.Temperature ratings may be for very low temperatures, ambienttemperatures, very high temperatures, and so forth.

FIG. 2 is a cross-section of the smart valve 10 taken along line 1-1 ofFIG. 1 that depicts the smart valve 10 in a closed position inaccordance with an embodiment of the present invention. The smart valve10 includes a valve stem 30 with a valve gate 32 attached to a lower end34 of the valve stem 30. In certain embodiments, the valve gate 32 maybe attached to the lower end 34 of the valve stem 30 via threading.However, in other embodiments, the valve gate 32 may be attached to thelower end 34 of the valve steam 30 using other connection methods, suchas T-slots, pins, lift nuts, and so forth.

The valve gate 32 may include a port 36 that allows process fluid flowthrough the valve body 12 when the valve gate 32 is moved to an openposition. In particular, the port 36 is an opening through the valvegate 32 such that, when the valve gate 32 is in an open position, theport 36 generally aligns with openings 38, 40 within an inlet seat 42and an outlet seat 44, respectively, of the valve body 12. By moving thevalve gate 32 axially along the central axis 20 of the smart valve 10such that the port 36 is aligned with the openings 38, 40 in the inletseat 42 and the outlet seat 44, the smart valve 10 may be opened and theprocess fluid may be allowed to flow through the valve body 12 of thesmart valve 10. Similarly, by moving the valve gate 32 axially along thecentral axis 20 of the smart valve 10 such that the port 34 is notaligned with the openings 38, 40 in the inlet seat 42 and the outletseat 44, the smart valve 10 may be closed. It should be appreciated thatthe smart valve 10 may be bi-directional, and the terms “inlet” and“outlet” are used for ease of reference and do not describe any specificdirectional limitation of the smart valve 10. For example, the seats 42,44 may be either inlet or outlet seats, respectively. It should also beappreciated that the location of the port 36 on the valve gate 32 isrelative. In general, the port 36 shown in FIGS. 2 through 4 is for afail-close valve. However, in other embodiments, the port 36 may bealigned with the openings 38, 40 to be a fail-open valve.

The flow path of the smart valve 10 is depicted by arrow 46. Inlet andoutlet valve connections 48, 50 may be used to couple the valve body 12of the smart valve 10 to process conduits or process piping. In theillustrated embodiment, the inlet and outlet valve connections 48, 50include flanges having inlet and outlet bolt holes 52, 54 for connectingto the process conduits or process piping (e.g., the upstream anddownstream pipe 26, 28 illustrated in FIG. 1). However, in otherembodiments, the inlet and outlet valve connections 48, 50 may be screwconnections, welded connections, and so forth.

As described above with respect to FIG. 1, the smart valve 10 mayinclude an actuator assembly 18. An actuator pressure control inlet 56may enable monitoring and control of the actuator pressure within apressurized cavity 58 within the actuator assembly 18. In particular, incertain embodiments, a pressurized fluid (e.g., air, oil, water, otherhydraulic fluids, and so forth) may be allowed to flow into and out ofthe pressurized cavity 58 through the actuator pressure control inlet56. A cylinder head 60 of the actuator assembly 18 may ensure that thepressure in the pressurized cavity 58 is retained. The pressurized fluidwithin the pressurized cavity 58 may exert the actuator pressure, whichmay be used to adjust or maintain the position (e.g., open or closed) ofthe valve stem 30 of the smart valve 10. In particular, the actuatorassembly 18 may operate much like a piston, wherein the actuatorpressure within the pressurized cavity 58 exerts a downward force ontoan upper surface 62 of a piston head 64 within the actuator assembly 18.

In general, this downward force may be resisted by actuator springs 66,which may generally extend from a lower surface 68 of the piston head 64to a lower inner wall 70 of the actuator assembly 18. In certainembodiments, the actuator springs 66 may be held in place such that theactuator springs 66 are only allowed to move axially. In other words,radial and tangential movement of the actuator springs 66 may beconstrained in these respective directions. For example, in certainembodiments, the actuator springs 66 may be held within cylindricaltubes, which also extend from the lower surface 68 of the piston head 64to the lower inner wall 70 of the actuator assembly 18.

As described above, the actuator pressure within the pressurized cavity58 may exert a downward force on the upper surface 62 of the piston head64, which may be resisted by the actuator springs 66, and the flowpressure may act on the valve stem 30 with other minor friction forces.As such, the interaction between the downward force exerted by theactuator pressure within the pressurized cavity 58 and the upward forcecreated by the resisting actuator springs 66 may determine the axialposition of the valve stem 30. In particular, an upper end 72 of thevalve stem 30 may be attached to the piston head 64. As the downwardforce created by the actuator pressure within the pressurized cavity 58overcomes the upward resistive force of the actuator springs 66, theflow bore pressure acting on the valve stem 30, and the friction forcebetween the surface of the valve gate 32 and the seats 42, 44, thepiston head 64 causes the valve stem 30 to move downward axially, forinstance, into an open position (see FIG. 3). However, as the upwardresistive force of the actuator springs 66 overcomes the downward forcecreated by the actuator pressure within the pressurized cavity 58, thepiston head 64 allows the valve stem 30 to move upward axially, forinstance, into a closed position. The relative upward and downwardforces and motion depicted in the illustrated embodiments are merelyillustrative and are not intended to be limiting. For example, in otherembodiments, the forces and motion may be in any direction where theresistive force from the actuator springs 66 generally counteracts theactuator pressure within the pressurized cavity 58.

As illustrated, the smart valve 10 may include a force sensor 74 (orload sensor) within the actuator assembly 18, which may be a load cell,strain gauge, and so forth. In general, the force sensor 74 may beattached to the valve stem 30 or may be integral with the valve stem 30and may generate data signals, which are indicative of the amount offorce exerted on the valve stem 30. As such, the force sensor 74 may beexternal to, and isolated from, the flow path 46 of the smart valve 10.In certain embodiments, a data wire 76 may be used to send the datasignals indicative of the force exerted on the valve stem 30 from theforce sensor 74 to a valve control system 78. The valve control system78 may include a processor and memory configured to execute programmablelogic. For example, the valve control system 78 may be a programmablelogic controller (PLC), a distributed control system (DCS), and soforth. In particular, as described in greater detail below, the valvecontrol system 78 may be configured to convert the data signalsindicative of the force exerted on the valve stem 30 into correlativepressures of the process fluid flowing through the valve body 12 of thesmart valve 10.

Also, in general, the data signals from the force sensor 74 may be usedto determine how to adjust the actuator pressure within the pressurizedcavity 58 of the actuator assembly 18. In particular, the valve controlsystem 78 may be configured to adjust the amount of pressurized fluid inthe pressurized cavity 58 of the actuator assembly 18 based at least inpart on the data signals generated by the force sensor 74. For instance,the valve control system 78 may include logic for determining when toincrease, decrease, or maintain the amount of pressurized fluid withinthe pressurized cavity 58. For, example, in certain embodiments, thevalve control system 78 may be configured to adjust the amount of thepressurized fluid is in the pressurized cavity 58.

In particular, in certain embodiments, the valve control system 78 maybe configured to determine whether to increase, decrease, or maintainthe amount of pressurized fluid within the pressurized cavity 58 byusing the data signals from the force sensor 74 to calculate thepressure of the process fluid flowing through the valve body 12 of thesmart valve 10. By using the force sensor 74 in this manner, thepressure of the process fluid may be determined without using obtrusive,direct measurement techniques, such as pressure gauges, pressuretransducers, or other pressure elements installed directly into the flowpath 46 of the process fluid.

In general, the pressure of the process fluid within the valve body 12of the smart valve 10 may be correlative to the stem force F_(stem)(e.g., the force experienced from the flow line pressure acting on thevalve stem 30). When the smart valve 10 is in the closed position, asillustrated in FIG. 2, the force sensor 74 may generally experience onlythe stem force F_(stem). One reason for this is that, when the smartvalve 10 is in the closed position, there may be a negligible amount ofpressurized fluid within the pressurized cavity 58 of the actuatorassembly 18, with the upper surface 62 of the piston head 64 abutting alower face 80 of an adjustment nut 82. The upward resistive force fromthe actuator springs 66 may react against the lower surface 68 of thepiston head 64 and, thus, against the lower face 80 of the adjustmentnut 82. However, in other embodiments, the actuator springs 66 may stillexert a certain amount of upward resistive force and the valve controlsystem 78 may be configured to adjust accordingly. As such, when thesmart valve 10 is in the closed position, the shut-in pressureP_(shut-in) may be estimated based at least in part on the forceF_(sensor) experienced by the force sensor 74. In particular, theshut-in pressure P_(shut-in) may be estimated by dividing the forceF_(sensor) experienced by the force sensor 74 by the cross-sectionalarea A_(stem) of the valve stem 30 using the equation:

P _(shut-in) =F _(sensor) /A _(stem)

As described above, once the actuator pressure is applied by addingpressurized fluid into the pressurized cavity 58 of the actuatorassembly 18, the resulting forces on the piston head 64 will cause thevalve stem 30 to move downward axially, such that the smart valve 10 ismoved toward its open position. FIG. 3 is a cross-section of the smartvalve 10 taken along line 1-1 of FIG. 1 that depicts the smart valve 10in an open position in accordance with an embodiment of the presentinvention. As illustrated, the actuator pressure caused by thepressurized fluid within the pressurized cavity 58 may exert an axiallydownward piston force F_(piston) distributed along the upper surface 62of the piston head 64. The piston force F_(piston) will generally bedistributed equally across the upper surface 62 of the piston head 64.In general, the resultant summation of the piston force F_(piston) willbe exerted onto the piston head 64 and, in turn, onto the valve stem 30,causing the valve stem 30 to move downward axially toward the openposition of the smart valve 10.

As described above, moving the valve stem 30 axially downward causes thevalve gate 32 to move axially downward as well. As such, the port 36within the valve gate 32 will begin aligning with the openings 38, 40within the inlet seat 42 and the outlet seat 44, respectively. When thishappens, the process fluid will begin flowing through the valve body 12of the smart valve 10 along the flow path 46. At some point, axialmovement of the valve stem 30 downward will be impeded by an upper end84 of a cylindrical stop 86, within which the valve stem 30 movesaxially. At this point, the smart valve 10 is in the fully open positionand, since the piston force F_(piston) is fully transferred to thecylindrical stop 86, the pressure of the process fluid P_(fluid) flowingthrough the smart valve 10 may be estimated based at least in part onthe force F_(sensor) experienced by the force sensor 74. In particular,the pressure of the process fluid P_(fluid) flowing through the smartvalve 10 may again be estimated by dividing the force F_(sensor)experienced by the force sensor 74 by the cross-sectional area A_(stem)of the valve stem 30 using the equation:

P _(fluid) =F _(sensor) /A _(stem)

In addition, in certain embodiments, performance characteristics of thesmart valve 10 may be estimated using the force F_(sensor) experiencedby the force sensor 74. In particular, the valve characteristics of thesmart valve 10 may be estimated while the smart valve is moved from aclosed position (e.g., FIG. 2) to an open position (e.g., FIG. 3). FIG.4 is a cross-section of the smart valve taken along line 1-1 of FIG. 1that depicts the smart valve transitioning from a closed position to anopen position in accordance with an embodiment of the present invention.Assuming the smart valve 10 is initially in a closed position, theactuator pressure may gradually be applied by adding pressurized fluidinto the pressurized cavity 58 of the actuator assembly 18. As describedabove, the piston head 64 may begin moving the valve stem 30 axiallydownward, causing the valve gate 32 to move from a closed to an openposition.

When the smart valve 10 is between the closed and open positions, theforce F_(sensor) experienced by the force sensor 74 may actually be asummation of multiple forces. More specifically, similar to the closedand open position scenarios, the force sensor 74 will experience thestem force F_(stem). However, in addition, the force sensor 74 will alsoexperience a gate drag force F_(gate) (e.g., the friction force of theclosed valve gate 32 acting against the valve seats 42, 44) and a springforce F_(spring) of the actuator springs 66 resisting the axiallydownward piston force F_(piston). When the upstream flow bore (e.g.,upstream of the valve gate 32) begins to connect to the downstream flowbore (e.g., downstream of the valve gate 32), the gate drag forceF_(gate) will diminish. Therefore, at this point, the force sensor 74will only experience the stem force F_(stem) and minor friction forcesexperienced at the valve gate 32 and the upper end 72 of the valve stem30. By monitoring the transition of these forces over time, the amountof the gate drag force F_(gate) may be used as an indicator of thecondition of the smart valve 10. In other words, monitoring these forcesover time may help determine valve signatures (e.g., indications ofoperating performance or other conditions) of the smart valve 10.

In certain embodiments, the valve gate drag force F_(gate) may beaccounted for by, for instance, subtracting the valve gate drag forceF_(gate) from the force F_(sensor) experienced by the force sensor 74.However, in other embodiments, the valve gate drag force F_(gate) may beassumed to be negligible. For example, as described above, when theupstream flow bore (e.g., upstream of the valve gate 32) begins toconnect to the downstream flow bore (e.g., downstream of the valve gate32), the valve gate drag force F_(gate) diminishes to a negligibleamount. The valve control system 78 may be configured to account for thevalve gate drag force F_(gate) when calculating the pressure P_(fluid)of the process fluid over time.

Optionally, in certain embodiments, a displacement transducer 88 may beinstalled to measure the axial displacement of the valve stem 30. Theaxial displacement data generated by the displacement transducer mayprovide additional information, in conjunction with the force datagenerated by force sensor 74, to provide additional indications of thevalve performance. As illustrated, in certain embodiments, thedisplacement transducer 88 may be located on an inner wall 90 of theactuator assembly 18 near the piston head 64 such that axial movement ofthe piston head 64 may be measured as a proxy for the axial displacementof the valve stem 30. However, the displacement transducer 88 may alsobe located at other positions within the smart valve 10. For example,the displacement transducer 88 may be placed in the actuator assembly 18to measure the displacement of the piston head 64, the valve stem 30, oreven the valve gate 32.

FIG. 5 is a flow chart of a method 92 for determining a pressure of theprocess fluid using the smart valve 10 in accordance with an embodimentof the present invention. At block 94, a position of the smart valve 10may be determined. For example, the smart valve 10 may be placed in anopen position (e.g., where the port 36 within the valve gate 32 isgenerally aligned with the openings 38, 40 within the inlet seat 42 andthe outlet seat 44). At block 96, a force exerted on the valve stem 30of the smart valve 10 may be measured. For example, as described above,the force F_(stem) exerted on the valve stem 30 may be measured by theforce sensor 74. At block 98, a pressure of the process fluid flowingalong the flow path 46 within the valve body 12 of the smart valve 10may be calculated. The process pressure may be correlative with theforce F_(stem) exerted on the valve stem 30 and may, in certainembodiments, be calculated at least in part by dividing the forceF_(stem) exerted on the valve stem 30 by the cross-sectional areaA_(stem) of the valve stem 30. Thus, without entry into the process flowpath 46, and thus avoiding potential leakage, the process pressure maybe determined using the method 92 of FIG. 5.

FIG. 6 is a flow chart of a method 100 for determining the performanceor other condition of the smart valve 10 in accordance with anembodiment of the present invention. At block 102, a position of thesmart valve 10 may be adjusted. For example, again, the smart valve 10may be adjusted to an open position (e.g., where the port 36 within thevalve gate 32 is generally aligned with the openings 38, 40 within theinlet seat 42 and the outlet seat 44). During the adjustment of thevalve position, at block 104, the forces exerted on the valve stem 30may be monitored, for instance, via the force sensor 74. Optionally, atblock 106, a displacement of the valve stem 30 relative to the flow path46 may be measured by the displacement transducer 84 positioned withinor adjacent to the smart valve 10.

With the data generated by blocks 102, 104 and 106, at block 108, avalve signature (e.g., an indication of operating performance or othercondition) may be determined based on the monitored forces. Then, atblock 110, this valve signature may be compared to previous valvesignatures to determine a change in condition or performance of thesmart valve 10 over time. Thus, the valve condition may be determinedvia the force sensor and optional displacement transducer.

Although discussed herein as applying to the particular type of gatevalve illustrated in FIGS. 2 through 4, other types of gate valves, suchas those with non-linear flow paths, may also take advantage of thedisclosed embodiments. Further, valve types other than gate valves mayalso benefit from the disclosed embodiments. For example, ball valvesmay utilize a force sensor and also optionally a displacementtransducer. Movement of the stem in the ball valve as well as movementof the ball may be monitored, and the pressure exerted on such elementsmay be measured. Such data may provide a signature of the valveindicative of operating performance and condition of the valve. Suchdata may also provide for measurement of the process fluid pressure.

While the invention may be susceptible to various modifications andalternative forms, specific embodiments have been shown by way ofexample in the drawings and have been described in detail herein.However, it should be understood that the invention is not intended tobe limited to the particular forms disclosed. Rather, the invention isto cover all modifications, equivalents, and alternatives falling withinthe spirit and scope of the invention as defined by the followingappended claims.

1. A valve, comprising: a body having a flow path; a stem; a flowelement coupled to the stem, wherein the flow element interfaces withthe flow path to regulate flow of a fluid through the flow path; and aforce sensor coupled to the stem and configured to indicate an amount offorce exerted on the stem.
 2. The valve of claim 1, wherein the amountof force indicated by the force sensor is correlative with a pressure ofthe fluid.
 3. The valve of claim 1, wherein the amount of forceindicated by the force sensor provides a signature of the valve.
 4. Thevalve of claim 1, wherein the force sensor comprises a load cell.
 5. Thevalve of claim 1, comprising an actuator configured to move the stem toadjust a position of the valve.
 6. The valve of claim 5, wherein theactuator comprises a piston configured to act against springs of theactuator to move the stem.
 7. The valve of claim 1, comprising adisplacement transducer configured to indicate displacement of the stem.8. The valve of claim 7, wherein the displacement is relative to theflow path.
 9. The valve of claim 7, wherein the displacement drivesadjustment of the flow element relative to the flow path.
 10. The valveof claim 7, wherein the displacement is substantially perpendicular to adirection of fluid flow through the flow path.
 11. A system, comprising:a conduit configured to transmit a fluid; a valve comprising: a bodyhaving a flow path; a stem; a flow element coupled to the stem, whereinthe flow element is disposed adjacent the flow path and operates toadjust a position of the valve; and a force sensor configured toindicate an amount of force exerted on the stem.
 12. The system of claim11, wherein the force exerted on the stem indicated by the force sensoris correlative with a pressure of the fluid.
 13. The system of claim 11,wherein the force exerted on the stem indicated by the force sensorprovides a signature of the valve over time.
 14. The system of claim 11,wherein the force sensor comprises a load cell.
 15. The system of claim11, comprising a displacement transducer configured to measuredisplacement of the stem or a piston head in an axial direction of thestem.
 16. The system of claim 15, wherein the displacement of the stemmeasured by the displacement transducer provides for a signature of theamount of the force on the stem as a function of the displacement.
 17. Amethod of determining a process pressure, comprising: determining aposition of a valve; measuring a force exerted on a stem of the valve;and calculating a process pressure correlative with the force exerted onthe stem.
 18. The method of claim 17, wherein the force exerted on thestem is measured with a force sensor.
 19. The method of claim 17,wherein the process pressure is calculated at least in part by dividingthe measured force by the cross-sectional area of the stem.
 20. Themethod of claim 17, comprising measuring displacement of the stemrelative to a flow path of the valve.